A 2-hydroxyester compound is an industrially important compound as intermediates of raw materials of medicine and pesticide or raw materials of photographic chemicals. As a method for producing a 2-hydroxyester compound, there is a method for using an amide, an alcohol and a formate ester as starting raw materials; a method for using a 2-hydroxycarboxylic acid and an alcohol; and also a method for using a cyanohydrin compound and an alcohol; or the like. Among these, because a cyanohydrin compound can be easily prepared from an aldehyde and hydrocyanic acid, various methods for producing a 2-hydroxyester compound by using a cyanohydrin compound as a starting raw material have been proposed.
For example, there is a method for producing 2-hydroxyfatty acid esters by a reaction of ketone cyanohydrin and sulfuric acid, followed by estrification of the reaction product and an alcohol, and by the addition thereto of an anhydrous sulfate salt of an alkali metal or the like (U.S. Pat. No. 2,041,820).
In addition, there is also a method for producing a 2-hydroxyester compound in high yield, by subjecting a cyanohydrin compound to a reaction with an acid such as hydrogen chloride or the like, in an alcohol solvent in a first step to synthesize a hydrochloric acid salt of an imino ether, followed by subjecting to hydrolysis by the addition of water, after removing an unreacted acid in a second step (JP-A-4-230241). In a conventional method according to a reaction among 2-hydroxynitriles, an alcohol and hydrogen chloride gas, reaction time is long such as from 12 to 15 hours, and continuous contact of the reaction mixture solution with HCl flow is required during the reaction, which makes operation troublesome and also provides low yield of an ester.

In addition, there is also a method for subjecting a specific cyanohydrin compound to a reaction with water and phosphoric acid, followed by esterification by the addition of an alcohol to the reaction product (JP-A-6-247895). The method is proposed in view of problems that co-occurrence of an etherification reaction of a hydroxycarboxylate ester, which is a reaction product, and an alcohol cannot be avoided, which results in contamination of an alkoxycarboxylate ester, as a byproduct, in a reaction product, when a strong acid such as sulfuric acid or hydrochloric acid is used as an acid, and the method features in using phosphoric acid. A reaction by using phosphoric acid proceeds in high selectivity, because side reactions, which generate etherified substances, are suppressed. As shown in the following formulae, the reaction aims at amidation by action of water and phosphoric acid to a cyanohydrin compound, followed by esterification by an alcohol.

In addition, there is also a method for esterification by subjecting specific amount of water and specific amount of sulfuric acid to a reaction with a specific cyanohydrin compound, followed by the addition of an alcohol to the reaction product (JP-A-6-247896). The method aims at proceeding the reaction in high selectivity by suppressing side reactions generating etherified compounds, by amidation by action of water and sulfuric acid to a cyanohydrin compound, followed by esterification with an alcohol, and while continuously supplying water-containing an alcohol to this reaction mixture, by distillating a hydroxycarboxylate ester generating at the same time.
It should be noted that, in the case where a cyanohydrin compound is used as a raw material, because a nitrogen atom composing a cyano group is reduced and finally converted to ammonia and discharged, ammonium sulfate, ammonium nitrate, ammonium phosphate, ammonium chloride or the like is by-produced corresponding to kind of an acid to be used. As a method for fractionating such an ammonium salt, for example, there is a method for recovering a 2-hydroxyester compound by distillation, by the addition of sodium sulfate to a slurry of a reaction solution containing an ammonium salt, an alcohol, a 2-hydroxyester compound and the like (U.S. Pat. No. 2,041,820), or a method for subjecting a slurry of a reaction solution to solid-liquid separation (JP-A-4-230241).